It is standard practice, as for example seen from my earlier U.S. Pat. No. 4,186,432 and patent application Ser. No. 084,194 filed Oct. 12, 1979 (now U.S. Pat. No. 4,312,018), to provide a fluorescent or cold-cathode light source in an enclosure formed by a base plate and a concave cover. This assembly is secured releasably to a support which is secured to the wall or roof of the mine. Electrical connections are made between the base plate and the support for energizing the light bulb.
It is essential that the light source be protected from the ever-present dust and moisture of the mine. To this end a tight seal must be provided between the base plate and the cover or lens to prevent the entry of moisture and dust.
As a rule this cover or lens is held in place on the base plate by a plurality of screws which must be painstakingly withdrawn in order to gain access to the light tube in order to change it. Obviously this makes changing the light bulb relatively complex. Accordingly it has been suggested to make the entire lamp assembly removable so that the user need merely take off the burnt-out light bulb with its base plate and lens and replace it with another such unit which may be secured in place by means which do not have to make a hermetic seal between the support and the lamp assembly.
Since it is a relatively inconvenient operation, even at a work table outside the mine, to take part the lamp assembly and put a new bulb into it, the above-described system has been found inadequate. Most often the lamp assemblies with burnt-out bulbs are simply discarded. Furthermore carting entire lamp assemblies down a mine and carting the lamp assemblies with burnt-out lamps back out is a procedure regarded by many mine operators as inefficient, compared to the ease with which fresh bulbs can be carried down, with the burnt-out light bulbs merely being discarded in the mine.